There have already been attempts to measure light absorption coefficients of deep portions using spatial resolution by multi-point measurement, however multiple solutions arise, and a solution cannot be derived. To address this, there is a known method for a muscle and fat structure in which a relationship between a spatial slope S and a muscle absorption coefficient pa is expressed by introducing a second order function. The absorption coefficient of muscle is then determined by adding a means to input the thickness of fat, and using a computation formula corresponding to the thickness (Patent Document 1). Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2007-139191.